High-speed active beam steering system and equipment operating in transmission mode

Abstract

The device comprises a dielectric substrate (DS) and a cover window (DCW), both of which are transparent; a number of transparent conductive rails (VEL) extending parallel to each other between the dielectric surfaces and dividing the space between the substrates into a number of elongated cells (LC0-LC3); a nematic liquid crystal (LC) loaded into the elongated cells; and a potential (V0-V N and a plurality of electrical interconnects (ELI) suitable for applying a voltage to the conductive rails, wherein the pitch P of the conductive rails is less than an optical wavelength λ, and the height H of the conductive rails is at least equal to λ / Δn, where Δn is the birefringence of the liquid crystal at the optical wavelength.

Description

[Technical Field]

[0001] This invention relates to beam steering equipment operating in a high-speed transmission mode (in the range between 100 kHz and several MHz). While not exclusive, it is particularly applicable to the field of LiDAR (Light Detection and Ranging). [Background technology]

[0002] LiDAR (Light Detection and Ranging) imaging systems enable the dynamic detection of distances to fast-moving objects and are considered a key technology for autonomous vehicles. LiDAR typically employs beam steering devices that direct a light beam in any direction to enable high-speed and highly efficient wide-field-of-view (FoV) spatial scanning. Current beam steering devices, operating in reflection or transmission modes, include, among others, mechanical laser scanners, integrated optical phased arrays (OPAs), microelectromechanical systems (MEMS) deflectors, acousto-optics (AO), and liquid crystal (LC) modulators. Each of these technologies has its own advantages and limitations. For example, - While mechanical laser scanners have a wide field of view (FoV), the use of mechanically moving parts makes them slow, large, complex, and vulnerable to mechanical failures. - Integrated OPAs based on waveguide arrays can achieve high scan frequencies (around MHz) and reasonable FoV (within 20 to 50 degrees), but they are complex and limited to low-power optical power due to insertion losses. - While AO deflectors can also achieve high modulation frequencies of around MHz, they are limited to small deflection angles (usually <2 degrees) and efficiency is limited to approximately 70%. - While MEMS modulators have a tolerable FoV (within 20-60 degrees), they are quite slow for LiDAR applications (scan frequencies in the kHz range), operate only in reflection mode, and offer limited flexibility in device integration.

[0003] Phase or amplitude LC modulators are particularly promising because they can operate in transmission mode. Furthermore, they are lightweight, operate at low control voltages (a few volts), and can be integrated on-chip. However, commercially available LC modulators have limited potential for LiDAR applications due to their low scan frequencies in the kHz range and their optical efficiency, which does not fully satisfy the wide deflection angles resulting from higher-order diffraction effects and relatively low FoV. Non-patent document 1 describes a state-of-the-art LC beam steering device operating in transmission mode.

[0004] Current optical deflectors based on nematic LC (or NLC) utilize the ability of these materials to adapt their optical properties to external stimuli, including temperature, electromagnetic fields, and mechanical stress. In particular, the application of voltage can induce a controllable phase delay relative to a transmitted beam, which is necessary to deflect light from its initial direction. NLC consists of positionally disordered elongated molecules statically oriented along a common macroscopic axis of symmetry (i.e., the N direction). NLC exhibits orientation-dependent physical properties but remains highly viscous like a normal liquid. When positive (negative) dielectric anisotropic NLC is confined between two electrodes, the application of voltage induces bulk elastic deformation, leading to collective rotation of LC molecules along (perpendicular to) the direction of the electric field. Uniform NLC reorientation requires LC that is perfectly aligned prior to the application of voltage. This is achieved when LC is placed near a mechanically or (photo)chemically treated solid surface to control its orientation at the interface via the so-called "anchor effect." When LC reorientation occurs, the LC free energy resulting from the antagonism between the electric force and the anchor force is minimized. LC molecules exhibit a uniaxial birefringence in the range of 0.05–0.45, and their optical axis is aligned with the longitudinal axis of the molecule.

[0005] As shown in Figure 1, conventional LC modulators use a micrometer NLC layer (reference LC modulator) confined between planar transparent electrodes. The bottom electrode, supported by a dielectric bottom substrate BS, is typically pixelated at a micrometer pitch (pixels PV0, PV1, PV2, PV3 are aligned in the "x" direction), while the top electrode RV0 is maintained at a reference voltage V0. A protective glass PG is also present above the top electrode. In the example in Figure 1, pixel PV0 is maintained at voltage V0, and therefore there is no electric field acting on the LC molecules. Due to the presence of an alignment layer that induces initial (voltage-free) alignment in the "x" direction parallel to the planar electrodes, the LC molecules remain aligned in the x direction. Pixels PV1, PV2, PV3 are maintained at increasing voltages V1, V2, V3, resulting in an increase in electric field strength and inducing gradual rotation of the LC molecules according to the pixel. At high voltages, LC molecules with positive dielectric anisotropy, such as pixel PV3, are aligned in the "z" direction perpendicular to the planar electrodes. The light beam LB, which propagates in the "z" direction and is polarized in the "x" direction, collides with the bottom electrode and is polarized at PV0. e A stepwise decrease in refractive index occurs, from an anomalous refractive index to n0 (normal refractive index) at PV3, resulting in beam deflection.

[0006] By investigating NLC compounds with optimal dielectric and viscoelastic properties for high-speed magnetic field-induced reorientation, the response time τ of an LC modulator to an electric field is primarily determined by the thickness (H) of the LC layer confined between the two electrodes. To accommodate the 2π phase shift required for full wavefront operation, the LC thickness H must be less than λ / Δn, and Δn = n e -n0 is the LC birefringence. As a result, for such conventional NCLs, τ is on the order of a few milliseconds. Furthermore, for LC modulators operating in the visible range, the separation of pixel electrodes by a spacing much larger than the incident wavelength leads not only to a narrow deflection angle but also to a high diffraction order, which negatively impacts the device efficiency. The fringing effect at the boundaries of adjacent pixels further increases the amount of light that produces a high diffraction order.

[0007] To support propagation modes, a metasurface-based transmissive optical deflector generates a refractive index gradient by employing high refractive index dielectric optical elements with subwavelength sizes and spacings that have a gradually changing lateral dimension in one direction but a sufficiently large thickness (~1 μm). Thus, a general law of refraction can be determined, and any deflection angle can be achieved by appropriately adjusting the phase discretization level provided by each metasurface repeating unit (Non-Patent Literature 2). The subwavelength topology of the metasurface suppresses high diffraction orders, resulting in high deflection efficiency and large deflection angles (greater than 60 degrees). The main limitation of metasurface-based deflectors is that they are designed and ultimately manufactured to deflect at a predetermined fixed angle, essentially functioning as passive optical elements. It has been proposed to fabricate tunable metasurfaces by using them in conjunction with LCs. For example, Patent Literature 1 discloses an optical deflector operating in reflection mode based on a metasurface formed by the conduction of linear nanoantennas with subwavelength widths and spacings. LCs are filled in the spaces between the nanoantennas. The voltage applied between adjacent nanoantennas controls the orientation of LC molecules and thus the electromagnetic environment of the nanoantennas. This has been demonstrated to enable control of the deflection angle. The drawbacks of this approach are that it only allows for reflection mode operation, is sometimes impractical from an integration standpoint, and limits the maximum achievable optical efficiency.

[0008] Non-patent document 3 describes another architecture for a tunable metasurface comprising dielectric nanopillars surrounded by a liquid crystal whose orientation is controlled by a voltage applied between upper and lower electrodes. This architecture enables beam steering in transmission mode, but its performance is not entirely satisfactory. The FoV does not exceed ±11°, the optical efficiency is around 35%, and the scan frequency is only slightly higher than that of conventional LC modulators. [Prior art documents] [Patent Documents]

[0009] [Patent Document 1] U.S. Patent Application Publication No. 2020 / 0303827

Non-Patent Literature

[0010]

Non-Patent Literature 1

Non-Patent Literature 2

Non-Patent Literature 3

Summary of the Invention

Problems to be Solved by the Invention

[0011] The present invention aims to overcome all or some of these drawbacks of the prior art. In particular, it aims to provide an integrated beam steering device that operates with high optical efficiency in a high-speed transmission mode and achieves a wide FoV (several degrees or several tens of degrees).

Means for Solving the Problems

[0012] According to the present invention, these objectives are achieved by arranging elongated transmission electrodes adjacent to each other at sub-wavelength distances. As a result, a collection of sub-wavelength gaps or "grooves" is obtained, which are individually activated by the penetration of NLC and the induction of NLC reorientation within the gaps by applying a potential difference. This approach has several advantages. The resulting sub-wavelength topology of the metasurface causes NLC sub-wavelength nanostructuring, suppressing high diffraction orders and thus producing high deflection efficiency. The vertical electrodes separating the cells avoid the fringe effect. The small distance between electrodes shortens the LC reaction time.

[0013] It is worthwhile to highlight the differences between the present invention and Patent Document 1. In the apparatus of Patent Document 1, the vertical electrode acts as a resonant nanoantenna, the LC constitutes its tunable dielectric environment, and the phase shift of the reflected light is determined by its interaction with the nanoantenna. In the present invention, the vertical electrode acts as a simple transmissive dielectric slab for optical radiation, and by utilizing the operating principle of conventional LC modulators, it experiences a phase shift only when confined within the LC.

[0014] The subject of this invention is a beam steering device according to claim 1.

[0015] Another subject of the present invention is a beam steering device according to claim 9.

[0016] A further subject of the present invention is the optical system according to claim 10.

[0017] Certain embodiments of the present invention constitute the subject matter of the dependent claims. [Brief explanation of the drawing]

[0018] Additional features and advantages of the present invention will become apparent from the subsequent description when interpreted in conjunction with the accompanying drawings. [Figure 1] Figure 1 shows the structure and operating principle of an LC beam steering device based on prior art that has already been considered. [Figure 2]Figure 2 shows the reorientation of LC molecules under the influence of an electric field, with respect to the initial (voltage-off) vertical alignment of LC molecules. [Figure 3] Figure 3 shows the change in NLC refractive index caused by x-polarization as a result of complete 90° reorientation. [Figure 4] Figure 4 shows a periodic pattern of 2π phase-shift elements that form a "supercell" and enable efficient deflection of the incident light beam. [Figure 5] Figure 5 is a side view showing an isolated 2π supercell that provides four (four) phase discretization levels by adjusting the refractive index of four NLC cells located between consecutive transmission vertical electrodes to convert the incident beam IB into a deflected beam DB. [Figure 6] Figure 6 is a schematic top view showing the apparatus, including the active area, which consists of periodically repeating transparent electrodes and LC cells, printed resistor contacts, and a drive circuit board. [Figure 7A] Figure 7A shows the difference in effective refractive index between a single hybrid electrode and an NLC pixel, depending on the electrode packing density (ff) per pixel, before voltage application and for maximum voltage-induced reorientation. [Figure 7B] Figure 7B is a grayscale color map showing the near-field electric field distributions that represent different pixel confinement modes (i.e., NLC and high refractive index electrodes, respectively) for electrode ff5% and 50% for each total pitch P. [Figure 8] Figure 8 shows the phase map obtained from a two-dimensional finite difference time-domain (2D FDTD) simulation of a single hybrid pixel and a transmission electrode width W when sweeping the NLC rotation angle θ (GaN is considered for the simulation, but other transparent and conductive materials may be considered). A phase shift of ~2π is obtained when W is ~100 nm or less. Using a different electrode material will change the value of W that causes a 2π phase shift. [Figure 9]Figure 9 shows the transmittance map obtained from a two-dimensional finite difference time-domain (2D FDTD) simulation of a single hybrid pixel and the transmittance electrode width W when sweeping the NLC rotation angle θ (GaN is being considered). When W is less than or equal to 100 nm, a transmittance close to 1 (unity (1)) is obtained. [Figure 10] Figure 10 shows how the deflection angle depends on the number of phase levels (M) that form the type of pattern shown in Figure 4. [Figure 11] Figure 11 shows the dependence of the device efficiency on the deflection angle. [Figure 12] Figure 12 shows one proposed two-dimensional beam steering device according to an embodiment of the present invention. [Modes for carrying out the invention]

[0019] In the following description, "light" refers to electromagnetic radiation in the mid-infrared (3 μm–50 μm), near-infrared (780 nm–3 μm), visible (380 nm–780 nm), or near-ultraviolet (200 nm–380 nm) ranges. Similarly, "optical wavelength" includes wavelengths in the mid-infrared (3 μm–50 μm), near-infrared (780 nm–3 μm), visible (380 nm–780 nm), and near-ultraviolet (200 nm–380 nm) ranges. Unless otherwise specified, wavelengths are measured in a vacuum.

[0020] An object can be considered "transmissive" at a given wavelength if its transmittance coefficient at that wavelength is not less than 0.9.

[0021] Figure 2 shows the complete electrical reorientation of positively dielectric anisotropic NLC between two perpendicular conductive and transparent rectangular electrodes EL (side view) forming a groove, labeled as LCI and LCF configurations. When no voltage is applied between the electrodes (VOFF), LC aligned normally to the subwavelength groove designed on the substrate SB is conceivable (i.e., NLC director in the y-direction). With the application of a high electric field (non-zero voltage VON), a 90° out-of-plane NLC reorientation along that direction results between voltage off (VOFF) and voltage on (VON). The VON state corresponds to the maximum applied electric field. Figure 3 shows the NLC refractive index n0 and n when the rotation angle of the NLC molecules changes between 0° (LCI configuration) and 90° (LCF configuration). e This indicates a smooth transition between the two.

[0022] Figure 5 shows that the SC (referred to as the "supercell" for reasons explained later with reference to Figure 4) portion of a beam steering device BSD according to an embodiment of the present invention comprises a dielectric substrate DS and a dielectric cover window (DCW) that are transparent at at least one optical wavelength. For example, these may be made of sapphire (Al2O3). The DS and DCW have parallel planar surfaces facing each other at a distance equal to at least the thickness H of the transparent vertical electrode (VEL), i.e., in the micrometer range. Hereinafter, the x and z directions parallel to the plane of the substrate are referred to as the "horizontal" directions, and the direction y perpendicular to the plane of the substrate and along the electrode thickness H is referred to as the perpendicular.

[0023] Multiple (five in Figure 5) conductive rails—or vertical electrodes VEL—extend vertically from the upper surface of the lower electrode DS to the lower surface of the upper DCW. These conductive rails extend in the z (or "vertical") direction—preferably linearly—and thus subdivide the space between the two substrates into a one-dimensional array of elongated cells (or one-dimensional pixels) arranged in the x direction and loaded with nematic liquid crystals, labeled LC0-LC3. The conductive rails are transparent at least in optical wavelength λ, and for example, they are used to transmit highly Si-doped (~10) cells epitaxially grown on the DS. 20 cm -3They can be made from GaN. The rail length can be several hundred microns or more.

[0024] A beam steering system (BSD) typically consists of multiple adjacent supercells.

[0025] The pitch P of the conductive rail—defined as the sum of the width of a single cell (measured in the x-direction) and the width of the conductive rail (also measured in the x-direction)—is less than the wavelength λ. For example, in the visible range, P is between 200 nm and 500 nm, while in the near-infrared range, it can extend over approximately 2 μm. The cell array does not need to be strictly periodic; if not, the pitch may vary in the x-direction.

[0026] Depending on the birefringence of NLC and the wavelength of the incident light, the aspect ratio H / W of the conductive rail is generally greater than 10, for example, about 15.

[0027] The dimensions of the BSD device are specifically defined by three parameters: H, P, and W.

[0028] As shown in Figure 6, the electrical wiring ELI supplies potentials V0, V1, V2 from one side of each transparent conductive rail TCR and from the opposite side to the rail voltage input channel VIC. N-1 ,V NIt can be individually connected to each port of a drive circuit board DCB (e.g., an integrated circuit) configured to apply a voltage, and accordingly reorient the continuous LC cells LCC located in the device active area DAA. The electrical wiring is made of any conductive material suitable for resistive contacts. For example, a copper or gold path on a printed circuit board contacts the conductive rail at one of its both ends. The latest electronic engineering technology facilitates the realization of such a high-density wiring pattern. For example, UV lithography is employed to design a specific wiring pattern that conforms to the active area of a device that can be manufactured by electron beam lithography (or deep ultraviolet lithography or nanoimprint lithography), and then electron beam metal evaporation, lift-off process, and ICP-RIE (inductively coupled plasma-reactive ion etching) etching are performed. According to an accurate ELI design, one or more DCBs can be considered. The drive circuit can be printed directly on the glass or connected to the device as an external panel (outside the glass). A drive algorithm can be used to adjust the desired voltage pattern provided by the continuous electrodes.

[0029] When two conductive rails enclosing a single NLC cell are maintained at different potentials, an electric field that changes the orientation of the liquid crystal molecules is generated in the cell, and due to NLC reorientation, the extraordinary effective refractive index that the light beam IB propagating in a propagation direction exactly or approximately aligned with the y-axis through the device and linearly polarized in the x-direction faces changes. However, the ordinary refractive index is not affected by the reorientation. This configuration has several advantages compared to the conventional one shown in FIG. 1. - Considering a specific NLC compound, for a given potential difference and anchor strength, the LC switching time is proportional to G 2 =(P-W) 2 and this is much smaller than H 2 resulting in high-speed operation - generally by one or two orders of magnitude, leading to an LC reorientation frequency of approximately 100 kHz - 1 MHz. - Adjacent cells are separated by a rigid wall portion, avoiding the fringe effect that induces losses. The subwavelength geometry of the cell in the -x direction suppresses high refractive orders that impart high deflection efficiency. In fact, electrically adjustable metasurfaces can be considered in the apparatus according to the invention. - For visible optical wavelengths, nanoscale confinement of LC molecules ensures high-quality and homogeneous alignment before electric field application. A related drawback is that this nanoscale confinement induces strong anchoring forces, requiring a broad electric field to overcome them, but for a given potential difference, the electric field increases as the pitch decreases. Depending on the geometric parameters of the transparent conductive metasurface, the physical properties of the LC (dielectricity, viscoelasticity), the strength of the interfacial interaction between the LC and the underlying metasurface, and voltage values ​​in the range of 1V–10V are appropriate for LC activation.

[0030] Regarding the "electric field-off state," liquid crystal molecules can be oriented in the y-direction. This initial (VOFF) alignment condition along the normal to the groove plane can be achieved by controlling the geometric parameters of the conductive and transparent metasurface (e.g., the aspect ratio of the electrodes), along with the interfacial interaction between the LC molecules and the transmitting electrode. Alignment layers can be applied to the upper and lower surfaces of the DS and DCW, respectively, to force perpendicular or other alignments. This can be achieved by employing conventional alignment techniques such as optical alignment and / or chemical alignment. Controllable out-of-plane (i.e., yx-plane) realignment of the LC optical axis can be induced by considering NLC with positive dielectric anisotropy by gradually increasing the voltage difference between two adjacent conductive rails, and therefore the strength of the electric field in the x-direction. This results in a refractive index n of light propagating in the y-direction and polarized in the x-direction. LC It undergoes a gradual change. More precisely, the refractive index n LC n0 (normal refractive index) to n e It gradually increases up to (anomalous refractive index):

[0031]

number

[0032] In the equation, θ is the angle formed by the optical axis of the LC molecule and the wave vector of the incident light, and this is an increasing function of the absolute value of the electric field intensity in the x direction. LC (0°) = n0 and n LC (90°) = n e It is easy to see that this is the case.

[0033] Figure 3 shows the change in the refractive index of LC (with positive dielectric anisotropy) faced by x-polarized light as a function of the out-of-plane rotation angle of LC induced by an external voltage (i.e., potential difference) between two conductive rails defining the cell of a beam steering device. Depending on the anchoring conditions at the NLC electrode interface prior to voltage application and the sign of the NLC's dielectric anisotropy, different in-plane or out-of-plane reorientation configurations are possible. For example, if the initial alignment is along the z-direction, LC with negative dielectric anisotropy can be selected as the tunable material. Another example is to consider the in-plane reorientation of molecules with positive dielectric anisotropy aligned along the groove axis (i.e., in the z-direction) prior to voltage application. The initial (VOFF) alignment conditions, the NLC reorientation mechanism, and the sign of the NLC's dielectric anisotropy must be appropriately considered for phase-limited and / or amplitude modulation. In general, NLC with negative dielectric anisotropy is not a very suitable option for phase-limited modulation compared to NLC molecules with positive dielectric anisotropy due to its lower dielectric anisotropy value. Low dielectric anisotropy will increase the LC response time to the applied voltage.

[0034] Assuming the conductive rail has a negligible width (W→0), the minimum cell thickness H can be determined by λ / Δn, and for the most common LC, Δn=n e -n0 is 0.2-0.4, enabling a perfect 2π phase delay. In fact, W is usually not negligible due to limitations induced by conventional nanofabrication methods, such as electron beams and nanoimprint lithography. Therefore, the effective refractive index n of the hybrid metasurface forming the device is important. eff is, n LC (θ) can be considered a weighted average of the refractive index of the conductive rail, and this is independent of the applied potential. As a result, the effective refractive index Δn effThe maximum achievable change is less than Δn. This view is important to the invention because avoiding electromagnetic confinement in the transmission electrode a priori is not trivial. Electromagnetic simulations show that Δn with respect to the rail filling rate of the cell eff The dependency W / P can be calculated. Figures 7 and 8 show Δn = 0.23 (n0 = 1.51 and n at 650 nm). e Nematic LC of (=1.74) and GaN grown on a sapphire substrate (at 650nm n GAN The results of such calculations for a conductive rail (=2.38) are shown, with λ=650nm and P=380nm. It can be seen that beam steering is possible due to the contribution of LC pixels for GaN packing densities of 25% (i.e., W=95nm) or less.

[0035] It should be noted that only confined electromagnetic modes may exist if the pitch of the structure is not too small compared to the wavelength. Ideally, P should be about half the operating wavelength of the material, taking into account both the feasibility of manufacturing the lateral dimensions of the solid metasurface and the control of the LC anchor strength at the interface with the metasurface, and the tolerance X should not exceed ±0.4λ (i.e., 40%), preferably ±0.2 (20%), and even more preferably ±0.1 (10%). This should be carefully considered if the device operates within the visible wavelength range.

[0036] Δn eff Figure 7 shows that it does not depend linearly on the GaN packing ratio ff. In practice, the mode distribution of electromagnetic radiation from the device must be examined. As seen in Figures 7A and 7B, for small GaN packing ratios (5% in the example in Figure 7A), the electric field modes are mainly confined in the LC.

[0037]

number

[0038] Therefore, for large GaN packing ratios (50% in the example in Figure 7B), the modes are almost confined to the conductive rails Δn eff<<Δn. The latter situation should be avoided to achieve a phase delay of 2π, as it requires the fabrication of a structure with an extremely difficult aspect ratio. The packing threshold can be defined as approximately 25%. This value can be changed by considering different degrees of refractive index contrast between the LC and the underlying transparent and conductive structure.

[0039] As shown in Figure 4, an optical phase shift equal to 2π can be introduced by phase gradient supercells SC1, SC2, SCN, specified by an integer exponent j increasing in the x-direction. Each supercell has the structure shown in Figure 5 and contains M pixels (M=4 in this example), also specified by an integer exponent i increasing in the x-direction. In the i-th pixel Pi of a typical supercell j, Δφ i =(2πi / M)=idφ M dφ M = 2π / M, and as a result, the discretized phase ramp over distance P·M ranges from 0 to 2π, where P is the pitch of one hybrid pixel. Repeats of the same supercell form a periodic "sawtooth" pattern with period P·M. As shown in Figure 10, the maximum efficient deflection of a normal incident light beam is achieved at a phase level of M=4 and decreases with increasing value of M. The angular resolution of a device containing M individually addressable and periodically repeating pixels—i.e., the minimum non-zero deflection—is given by θmin=sin -1 (λ / MP). The maximum deflection angle is θmax = sin -1 It is determined by (λ / 4P). For a cell with a pitch of 380 nm and operating at λ=650 nm,

[0040]

number

[0041] As a result, FoV is approximately 50°. As can be estimated from Figure 7A, 25% GaN ff is Δn effCorresponding to ~0.17, and therefore lower than the NLC birefringence Δn ~0.23 considered, in which case the deflection operation of the device can be guaranteed for height H ~ λ / Δn by considering at least four (4) phase discretization levels. For manufacturing convenience, the phase discretization is from H to H ~ λ (2π-dφ i ) / 2πΔn eff This allows for a reduction in cell thickness up to a certain point.

[0042] In Figure 10, the black squares correspond to the results of a 2D FDTD simulation with a 45.6 μm long apparatus in the x-direction and a normal incident plane wave polarized in the periodic direction of the apparatus. The continuous lines correspond to theoretical calculations performed using "General Snell's Law" according to Non-Patent Literature 2. The very good agreement between the results confirms that the apparatus of the invention actually acts as an NLC metasurface.

[0043] Figure 11 shows that the optical efficiency (calculated using the 2D FDTD method) reaches 85%, and decreases due to the increase in the deflection angle.

[0044]

number

[0045] Even so, it shows that it maintains a fairly satisfactory value of ~65%, which is generally about three times higher than the efficiency achieved by devices operating in reflection mode. An optimization algorithm that can improve the efficiency obtained for the best deflection angle by local voltage adjustment can be incorporated into the deflector's drive algorithm. The latter can also be used to compensate for design imperfections resulting from the manufacturing process employed.

[0046] Due to their ability to operate in transmission mode and their high efficiency (Figures 9 and 11), two beam steering devices according to the present invention, having non-parallel (and preferably perpendicular) conductive rails, can be coupled to achieve two-dimensional beam steering. Figure 12 shows an optical system comprising a light source LS (e.g., a semiconductor laser with a sighting optical element) that generates an incident light beam ILB propagating in the y direction and polarized in the x direction, directed towards a two-dimensional beam steering device BSA. The two-dimensional beam steering device BSA comprises a first beam steering device BSD1, whose conductive rails are aligned in the z direction to deflect the beam ILB by an angle θ in the xy plane, and a second beam steering device BSD2, separated from BSD1 by a distance d in the y direction, whose conductive rails are aligned in the x direction to deflect the beam DLB1 by an angle φ to form a DLB2 in the distant yz plane. Due to the deflection-dependent response of the LC to its specific anchor configuration, designing a cascaded two-dimensional beam steering system is not straightforward. To achieve a predetermined deflection in two dimensions, the user must make technical choices—for example, the use of LCs with positive or negative anisotropy, the selection of an LC reorientation mechanism, the determination of the initial anchor direction at zero volts and the relative groove orientation of BSD1 and BSD2, and the selection of incident polarization.

[0047] Designers often try to avoid birefringence separation of the light beam. This is achieved by selecting the input polarization and incident angle of the light impacting each modulator to maximize the deflection efficiency at each modulator. In particular, in this case, the incident polarization to BSD1 must be selected to maximize the change in refractive index during LC reorientation. As an example, consider a first modulator BSD1 in which out-of-plane LC reorientation is electrically tuned by NLC molecules with positive dielectric anisotropy, anchored along the normal to the groove surface in the voltage-off state. In this case, the incident polarization must be perpendicular to the groove axis. From the design and incident polarization of BSD1, information can be obtained about the design and LC type to be selected for BSD2. Since the anomalous refractive index is affected by the applied voltage, the light incident to BSD2 must be polarized in the same plane as the NLC optical axis in BSD2. As an example, consider that the grooves of BSD2 are at a 90° angle to these BSD1s, meaning that the initial NLC orientation is normal to or parallel to that axis. As previously mentioned, assuming that the incident polarization at BSD2 maximizes the deflection after BSD1, the reorientation mechanism at BSD2 must be selected to maximize the deflection efficiency after BSD2. For example, if out-of-plane reorientation occurs at BSD2, the non-normal incident light colliding with it must exhibit a polarization projection that the NLC receives in a direction where phase modulation occurs during electrical reorientation. In such cases, an NLC with negative dielectric anisotropy is required. The voltage pattern applied to BSD2 must be increased or decreased as appropriate according to the target deflection angle and efficiency.

[0048] Other different design strategies could include, for example, maintaining only 1D deflection from either BSD1 or BSD2, modulating transmission efficiency, or separating incident light into several transmission and deflection output channels. The latter can be achieved by considering rotational polarization, or by relative rotation of BSD1 and BSD2 according to a specific LC type, anchoring conditions, and reorientation mechanism.

[0049] Although the present invention has been described with reference to specific embodiments, several modifications are possible. For example, various individual LC compounds or mixtures of several compounds having molecular structures that exhibit one or more LC phases with temperature changes (nematic, smectic, etc.), or possess diverse physical properties such as elastic constants of various values, rotational viscosity, dielectric anisotropy, birefringence, etc., can be considered as tunable materials. LC can penetrate the apparatus by capillary action in an isotropic liquid phase or in a vacuum permeation state. Furthermore, the present invention can also be carried out for phase only and / or amplitude modulation. In the latter case, the apparatus must be placed between the polarizer and the analyzer. For the solid metasurface, any optically transparent and conductive material can be used, one example being highly doped n-doped GaN, but doped polymers, or, not limited to, transparent conductive oxides such as ITO, can also be employed. Different materials than those specifically mentioned may be used for the dielectric substrate. Similarly, the dimensions for H, P, and W and the operating wavelength are presented only as non-limiting examples. Furthermore, the apparatus can operate at ambient temperature or other temperatures.

[0050] In some applications, the electrical substrates (DS,DCW) do not need to be planar; for example, the DS may have a convex top surface and the DCW a concave bottom surface, defining a curved, shell-like space. The conductive rails do not need to be perfectly straight and equally spaced, but high-quality LC alignment must be ensured prior to voltage application. To achieve this, specific (photo)chemical or mechanical treatments may be considered relevant materials that control the alignment characteristics of NLC at the interface. [Explanation of Symbols]

[0051] PG protective glass RV0 Reference electrode corresponding to voltage input V0 LC LCD BS bottom board Pixel electrode corresponding to voltage input V0 PV0 PV1 Pixel electrode corresponding to voltage input V1 Pixel electrode corresponding to voltage input V2 PV2 Pixel electrode corresponding to voltage input V3 PV3 LB Light Beam VOFF Voltage Off VON voltage ON corresponding to the maximum voltage value EL electrode SB board LCI (Liquid Crystal Indicator) Initial State (Voltage Off) LCF LC final state (maximum voltage on) VEL vertical electrode DCW Dielectric Cover Window DS dielectric substrate IB Incident Beam DB deflection beam LC0 is a liquid crystal cell in which the colliding polarized light typically exhibits a refractive index n0. LC1: Refractive index n of the colliding polarized light eff 1 (n0 <n eff 1 <n e ) corresponding LCD cell LC2 collision with polarized light with refractive index n eff 2 (n0 <n eff 1 <n eff 2 <n e ) liquid crystal cells LC3 anomalous refractive index n in colliding polarized light e liquid crystal cells that are produced DCB drive circuit board VIC Voltage Input Channel DAA Device Active Area LCC LCD Cell TCR transparent conductive rail ELI Electrical Wiring LS light source ILB Incident Light Beam DLB1 deflected light beam in the xy plane Deflected beam in the DLB2 yz plane H Height (or thickness) W width P: Pitch (or period) G gap or width between liquid crystal cells d distance SC, SC1, SC2, SCN Supercell

Claims

1. An active beam steering system (BSD), A dielectric substrate (DS) and dielectric cover window (DCW) that are transparent to one optical wavelength λ, wherein a dielectric substrate (DS) and dielectric cover window (DCW) define a space between them, To divide the space into a plurality of elongated cells (LCCs), a plurality of conductive rails (V) are formed, which are transparent to the optical wavelength and extend parallel to each other between the surface of the dielectric substrate (DS) and the surface of the dielectric cover window (DCW). ｏ -V Ｎ )and, The nematic liquid crystal (LC) is filled into the aforementioned elongated cell, A potential (V) is applied to each of the conductive rails. ０ -V Ｎ Multiple electrical wirings (ELI) suitable for applying ) and Equipped with, The pitch P of the conductive rail is smaller than the optical wavelength λ, A beam steering device in which the height H of the conductive rail is λ / Δn or greater, and Δn is the birefringence of the nematic liquid crystal at the optical wavelength.

2. The beam steering device according to claim 1, wherein the width W of the conductive rail is sufficiently small compared to the pitch P, and the light of the optical wavelength λ can be confined in the nematic liquid crystal filled in the elongated cell.

3. The beam steering device according to claim 1 or claim 2, wherein P = λ / 2 ± λX, where P is the pitch of the conductive rail, λ is the optical wavelength, and X is 0 to 40%.

4. The beam steering device according to claim 1 or claim 2, wherein the pitch P is in the sub-micrometer range.

5. The beam steering device according to claim 1 or claim 2, wherein the conductive rail is made of Si-doped GaN.

6. The beam steering device according to claim 1 or 2, further comprising an electronic drive circuit board (DCB) configured to apply a variable potential value to the conductive rail through the electrical wiring, wherein the potential difference between two adjacent conductive rails determines the phase shift of light of wavelength λ introduced by the elongated cell defined by the conductive rails.

7. The beam steering device according to claim 6, wherein the electronic controller is configured to apply a spatial periodic pattern of potential to the conductive rails such that the potential difference between two adjacent rails changes monotonically between zero and a maximum value, the maximum value being equal to 2π, where the phase shift of light of wavelength λ introduced by the elongated cells formed corresponding to the two adjacent rails.

8. The beam steering device according to claim 7, wherein the electronic controller is configured to change the deflection angle of a light beam of wavelength λ by changing the spatial period of the spatial period pattern.

9. A two-dimensional beam steering device (BSA) comprising a first (BSD1) and a second (BSD2) beam steering device according to the apparatus described in claim 1, The first and second beam steering devices are arranged such that the light beam (LB) traversing the first beam steering device (BSD1) collides with the second beam steering device (BSD2) and are suitable for operating at the same optical wavelength λ. The first and second beam steering devices are two-dimensional beam steering devices (BSAs) having conductive rails extending in non-parallel directions.

10. An optical system comprising a light source (LS) and a beam steering device (BSD) according to claim 1 or a two-dimensional beam steering device (BSA) according to claim 9, wherein the light source is configured to direct a light beam (LB) of optical wavelength λ toward the beam steering device or the two-dimensional beam steering device.

11. The two-dimensional beam steering device (BSA) according to claim 9, wherein the conductive rails of the first and second beam steering devices extend in a vertical direction.

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